Calculation method for shear strength of easily cuttable segments

Abstract

To provide a method of calculating shear capacity of easy machinable segment than can reasonably calculate a sear capacity for an easy machinable segment in which steel fibers are distributed in concrete and a shear reinforcement bar whose modulus of elasticity is smaller than that of a steel bar (steel stock) is applied.SOLUTION: There is provided a method of calculating a shear capacity of easy machinable segment 10 in which a reinforcement material 20 formed of a fiber reinforced plastic is embedded inside concrete as base material and steel fibers 30 are distributed inside the base material, and the reinforcement material 20 includes a main reinforcement 21 and a shear reinforcement 22. A shear capacity of the concrete in which the steel fibers 30 are distributed and a shear capacity of the shear reinforcement 22 whose modulus of elasticity is smaller than that of the steel fibers 30 are calculated, and both of the shear capacity are added to obtain a shear capacity of the easy machinable segment 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for calculating the shear strength of a machinable segment. [Background technology]

[0002] For example, after constructing the main tunnel and ramp tunnel separately using the shield method, an underground widening section is constructed by cutting and widening a portion of the main tunnel and ramp tunnel using non-open cut construction, and the two tunnels are connected at this underground widening section. The main tunnel is an underground passageway located at a great depth of, for example, 40m or more below ground, and a ramp tunnel is extended from this underground passageway, accessed from an aboveground interchange junction, etc., and the two tunnels are connected at the underground widening section. In constructing this underground widening section, the main tunnel and ramp tunnel, which are spaced apart, are surrounded by, for example, a cylindrical underground structure with a relatively large cross section, and then the inside of the underground structure is excavated and the connecting section between the two tunnels is removed to construct the underground widening section. When constructing the underground structure, waterproofing treatment is carried out in the construction area of ​​the underground structure as necessary. One method for constructing the above-mentioned large-section underground structure involves constructing an outer shell (large-section lining) by lining up multiple small-section tunnels in a cylindrical shape. More specifically, multiple preceding small-section tunnels are constructed in a circular shape at intervals, and then multiple following small-section tunnels are constructed in a circular shape at those intervals while cutting out portions of the preceding small-section tunnels, and portions of the following small-section tunnels are removed to connect them to the preceding small-section tunnels. In other words, a large-section lining is formed in which the preceding and following small-section tunnels are alternately strung together, connecting the small-section tunnels. Then, main reinforcement extending circumferentially is placed in the circular connecting portions of the large-section tunnels, and fill concrete is placed, thereby constructing the underground structure, which is the large-section lining. The preceding small-section tunnel and the following small-section tunnel that form the large-section lining are both constructed sequentially using the shield tunneling method. The preceding small-section tunnel, a portion of which is excavated by the following small-section tunnel, may be constructed using, for example, reinforced concrete (RC) segments, while the following small-section tunnel may be constructed using, for example, steel segments. Of these, it is desirable to use easy-to-cut segments that can be cut by a shield machine used to construct the following small-section tunnel for the segments that form the preceding small-section tunnel.

[0003] Patent Document 1 proposes a cutting segment using concrete as a base material and resin reinforcing bars, in which the concrete contains aggregate, the aggregate including coarse aggregate and fine aggregate, the coarse aggregate being lightweight aggregate or blast furnace slag aggregate, and the reinforcing bars being glass fiber rods with continuous threads. In this cutting segment, 0.25 to 0.5 volume % of aramid fiber is mixed into the concrete as an additive to prevent crack propagation.

[0004] According to the cut segment described in Patent Document 1, the inclusion of 0.25% to 0.5% by volume of aramid fibers can prevent crack propagation. However, it is unclear whether the incorporation of only 0.5% by volume of low-rigidity aramid fibers can effectively prevent crack propagation. Furthermore, the document makes no mention of the problem of cracks concentrating in one location (or as few locations as possible), increasing their width and reducing the watertightness of the cut segments, and naturally does not mention any means for solving this problem. Furthermore, it is extremely difficult to disperse cracks, reduce the crack width of each crack, and improve watertightness by simply incorporating 0.5% by volume of low-rigidity aramid fibers. Therefore, it is difficult to say that the characteristic configuration described in Patent Document 1 is effective in improving the crack dispersion and watertightness of the cut segments.

[0005] Therefore, Patent Document 2 proposes an easy-to-cut segment that is as inexpensive to manufacture as possible and has excellent cutting ability, load resistance, and water-stopping properties. Specifically, reinforcing bars made of fiber-reinforced plastic are embedded inside the base material, concrete, and steel fibers are dispersed inside the base material. The base material concrete has a design standard strength of 42 N / mm. 2 ~60N / mm 2 The mixing ratio of steel fiber is in the range of 0.3 volume % to 1.0 volume %, and the elastic modulus of the fiber reinforced plastic is 30 kN / mm 2 ~120kN / mm 2 is in the range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-49191 [Patent Document 2] Patent Publication No. 2021-195812 Summary of the Invention [Problem to be solved by the invention]

[0007] According to the cutting segment described in Patent Document 2, it is possible to provide an easy-to-cut segment that is produced at the lowest possible cost and has excellent cutting ability, load resistance, and water-stopping properties. The shear strength formula for concrete structures in which continuous fiber reinforcement is embedded in the concrete instead of steel bars is specified in Concrete Library 88, Design and Construction Guidelines for Concrete Structures Using Continuous Fiber Reinforcement (Draft), September 1996, Japan Society of Civil Engineers (hereinafter referred to as "Design Guidelines 1"). On the other hand, the shear strength formula for steel fiber reinforced concrete members, where concrete members are reinforced with steel fibers, is specified in Concrete Library 97, Design Guidelines for Steel Fiber Reinforced Concrete Column Members (Draft), November 1999, Japan Society of Civil Engineers (hereinafter referred to as "Design Guidelines 2").

[0008] In other words, when calculating the shear strength of an easily cuttable segment in which steel fibers are dispersed within the concrete, there is no method of calculating the shear strength of the concrete in which the steel fibers are dispersed and the shear strength of the shear reinforcement embedded in the concrete, which has a lower elastic modulus than the steel fibers (steel), and then calculating the overall shear strength of the easily cuttable segment based on these calculation results.For example, Design Guideline 1 does not take into account concrete in which steel fibers are dispersed, and only presents a calculation formula assuming the use of high-modulus carbon fiber reinforced plastic (whose elastic modulus is equivalent to that of steel bars), while Design Guideline 2 makes no mention of the use of reinforcing materials such as glass fiber reinforced plastic rods, which have an extremely small elastic modulus, about one-third that of steel bars, as shear reinforcement instead of steel bars.

[0009] The present invention aims to provide a method for calculating the shear strength of easily cuttable segments, which can rationally calculate the shear strength of easily cuttable segments in which steel fibers are dispersed in concrete and shear reinforcement bars with a smaller elastic modulus than steel bars (steel) are applied. [Means for solving the problem]

[0010] In order to achieve the above object, one aspect of the method for calculating the shear strength of a machinable segment according to the present invention is to: A method for calculating the shear strength of an easily cuttable segment in which reinforcing bars made of fiber-reinforced plastic are embedded inside concrete, which is a base material, and steel fibers are dispersed inside the base material, and the reinforcing bars include main bars and shear reinforcement bars, The shear strength of the concrete in which the steel fibers are dispersed and the shear strength of the shear reinforcement bars, which have a smaller elastic modulus than the steel fibers, are calculated separately, and the shear strength of both are added together to determine the shear strength of the easily cuttable segment.

[0011] According to this aspect, in calculating the shear strength of an easily cuttable segment in which shear reinforcement bars with a lower elastic modulus than the steel fibers (steel materials) are embedded inside concrete in which steel fibers are dispersed, the shear strength of the concrete in which the steel fibers are dispersed and the shear strength of the shear reinforcement bars with a lower elastic modulus than the steel fibers are calculated separately, and the shear strength of the easily cuttable segment can be calculated rationally by applying a method of adding up the shear strengths of both. The rationality of calculating the shear strength of the entire cuttable segment by adding up the shear strengths of both is based on the results of verification by the present inventors.

[0012] Another aspect of the method for calculating the shear strength of a machinable segment according to the present invention is as follows: Shear strength shared by the concrete in which the steel fibers are dispersed: V c is calculated using the following formula (A), and the shear strength shared by the shear reinforcement is: V s is calculated by the following formula (B), and the shear strength of both is added up to obtain the shear strength of the easy-to-cut segment: V u It is characterized by calculating the following.

[0013]

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[0014]

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[0015] According to this aspect, the shear strength of the concrete in which the steel fibers are dispersed is: V c Calculate the shear strength of the shear reinforcement, which has a smaller elastic modulus than the steel fiber (steel material): V s By calculating using formula (B), the shear strength of the easily cuttable segment: V uBoth formula (A) and formula (B) are modifications of existing formulas, taking into account the above-mentioned design guidelines 1 and 2. In formula (A), the reinforcing effect of steel fiber is evaluated by κ (1.0 or more). In addition, the dowel effect of the main reinforcement (main reinforcement) is evaluated by β p This reflects the elastic modulus of reinforcing bars made of fiber reinforced plastics (excluding high-elasticity carbon fiber reinforced plastics), which have a smaller elastic modulus than steel fibers.

[0016] In another aspect of the method for calculating the shear strength of a machinable segment according to the present invention, The reinforcing bars are made of one of glass fiber reinforced plastic rods, aramid fiber reinforced plastic rods, and medium elasticity carbon fiber reinforced plastic rods.

[0017] According to this aspect, the reinforcing bars are formed of rods such as glass fiber reinforced plastics (GFRP), and therefore no reinforcing bars made of expensive high-elasticity carbon fiber reinforced plastics are used. This reduces the manufacturing cost as much as possible, and the rods have low rigidity (the elastic modulus is 30 kN / mm 2 ~120kN / mm 2 The shear strength of the machinable segments, which have excellent machinability due to their range of shear strength, can be calculated.

[0018] Another aspect of the method for calculating the shear strength of a machinable segment according to the present invention is as follows: This method is characterized by applying the minimum amount of shear reinforcement specified in the 2017 Japan Society of Civil Engineers Standard Specifications for Concrete [Design Edition] without increasing the minimum amount of shear reinforcement by multiplying it by the reciprocal of the ratio of the stiffness of the reinforcement to the stiffness of the steel bar.

[0019] According to this aspect, even though fiber-reinforced plastics, which have a smaller elastic modulus than steel fibers, are used as shear reinforcement, by appropriately evaluating the reinforcing effect of steel fibers, excessive shear reinforcement can be prevented by applying the specified minimum shear reinforcement amount without increasing the minimum shear reinforcement amount specified in the Standard Specifications for Concrete [Design Edition] established by the Japan Society of Civil Engineers in 2017 (hereinafter referred to as "Design Guideline 3") by multiplying the reciprocal of the ratio of the stiffness of the reinforcing bars to the stiffness of the steel bars. The fact that there is no need to increase the minimum shear reinforcement amount is based on the results of verification by the present inventors.

[0020] Another aspect of the method for calculating the shear strength of a machinable segment according to the present invention is as follows: The minimum amount of shear reinforcement is a reinforcement ratio of 0.15%, which is the ratio of the cross section of the shear reinforcement to the cross section of the concrete.

[0021] According to this embodiment, even though fiber-reinforced plastic, which has a smaller elastic modulus than steel fiber, is used as shear reinforcement, the minimum amount of shear reinforcement is set to the reinforcement ratio of 0.15% as specified in Design Guidelines 1 and 3, thereby preventing excessive shear reinforcement.

[0022] Another aspect of the method for calculating the shear strength of a machinable segment according to the present invention is as follows: When the reinforcing bar is a glass fiber reinforced plastic rod, the elastic modulus of the reinforcing bar is 200 N / mm 2 The elastic modulus of the glass fiber reinforced plastic rod: 60 N / mm 2 The ratio is 0.3.

[0023] According to this embodiment, even if the reinforcing bar is a glass fiber reinforced plastic rod and the ratio of the elastic modulus to the steel bar is 0.3, the minimum amount of shear reinforcing bar is not increased from the reinforcing bar ratio of 0.15% specified in Design Guidelines 1 and 3 by an amount corresponding to this ratio (an increase by dividing by 0.3) to 0.5%, but by setting the reinforcing bar ratio at 0.15% specified in Design Guidelines 1 and 3, excessive shear reinforcement can be prevented. [Effects of the Invention]

[0024] According to the method for calculating the shear strength of easily cuttable segments of the present invention, it is possible to rationally calculate the shear strength of easily cuttable segments in which steel fibers are dispersed within the concrete and shear reinforcement bars with a smaller elastic modulus than steel bars (steel materials) are applied. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is an oblique view showing a cuttable segment to which an example of a shear strength calculation method according to an embodiment is applied, and is a transparent view that allows the interior to be seen. [Figure 2] FIG. 1 is a graph showing the tensile stress-strain relationship of various reinforcing bars. [Figure 3] FIG. 1 is a perspective view of an example of a steel fiber. [Figure 4] 1 is a schematic diagram of a test specimen used in a shear test. [Figure 5] FIG. 1 is a graph showing a load-displacement relationship obtained by a shear test. [Figure 6] FIG. 1 is a diagram showing the state of fracture of a test specimen in a shear test. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, a method for calculating the shear strength of a machinable segment according to an embodiment will be described with reference to the accompanying drawings. Note that in this specification and the drawings, substantially identical components may be designated by the same reference numerals to avoid redundant description.

[0027] [Method for calculating shear strength of easily cuttable segments according to the embodiment] First, an example of a method for calculating the shear strength of a machinable segment according to an embodiment will be described together with an example of a machinable segment to be calculated, with reference to Figures 1 to 3. Here, Figure 1 is a perspective view showing a machinable segment to which an example of a method for calculating the shear strength according to an embodiment is applied, and is a see-through view that allows the interior to be seen. Also, Figure 2 is a diagram showing a tensile stress-strain relationship graph for various reinforcing bars, and Figure 3 is a perspective view of an example of a steel fiber.

[0028] The machinable segment 10 designed and manufactured using the shear strength calculation method according to the embodiment has, inside the base material concrete, reinforcement members 21, 22 made of fiber-reinforced plastic and a large number of dispersed steel fibers 30. The machinable segment 10 has a curved shape that has the curvature of the segmented tunnel to be constructed, and has a pair of ring joint surfaces 11 and a pair of segment joint surfaces 12.

[0029] The design strength of the concrete base material is 42N / mm 2 ~60N / mm 2 The strength of the concrete applied to the segments is within the range of 100% and satisfies the design standard strength of the concrete specified in Design Guideline 3.

[0030] As shown in Fig. 1, main reinforcements 21 (inner main reinforcements and outer main reinforcements) that provide tensile resistance to the bending moment acting on the cuttable segment 10, and shear reinforcement 22 are arranged within the base concrete. Here, each of the reinforcements 21, 22 is made of fiber reinforced plastic, and more specifically, is made of one of glass fiber reinforced plastic (GFRP) rods, aramid fiber reinforced plastic (AFRP) rods, and medium elasticity carbon fiber reinforced plastic (medium elasticity CFRP) rods, and high elasticity carbon fiber reinforced plastic rods are not used.

[0031] As shown in Figure 2, the elastic modulus of these fiber-reinforced plastics is 30 kN / mm 2 ~120kN / mm 2 The elastic modulus is in the range of 200 kN / mm 2 The rods have lower rigidity than steel bars or high-elasticity carbon fiber reinforced plastics with an elastic modulus equivalent to that of steel bars. In this way, by using reinforcing bars 21, 22 made of low-rigidity rods, the machinability of easy-to-cut segment 10 is improved. Furthermore, by not using high-elasticity carbon fiber reinforced plastics, which are expensive materials, the manufacturing cost of easy-to-cut segment 10 can be kept as low as possible.

[0032] However, when only the reinforcing bars 21, 22 made of rods such as glass fiber reinforced plastic are embedded in the base material, the low rigidity of the rods makes it easier for large cracks to occur, which can reduce watertightness. Therefore, the easy-to-cut segment 10 employs a configuration in which a large number of steel fibers 30 are dispersed in the base material. For example, the steel fibers 30 are dispersed in the base material at a mixing rate of 0.3 to 1.0 volume %.

[0033] As shown in Figure 3, the steel fibers 30 have a straight central bar 31 and one or more stepped hook members 32 at both ends of the central bar 31. By having one or more stepped hook members 32 at both ends of the straight central bar 31, the steel fibers 30 have increased adhesion to the base material, improving the stress-strain characteristics of the machinable segment 10, which includes reinforcing bars 21, 22 made of low-rigidity fiber-reinforced plastic. In addition, the bridging effect of the steel fibers 30 improves crack dispersion, minimizing the crack width of potential cracks and improving watertightness.

[0034] Here, the steel fiber 30 has a strength of 1800 N / mm 2It is preferable to use high performance steel fiber (HPSF) having a high tensile strength. The stepped hook material 32 of the steel fiber 30 in the illustrated example has a substantially Z-shape, but stepped hook materials of various shapes and forms can be used, such as multi-stage stepped hook materials with two or more substantially Z-shapes. Furthermore, the central rod 31 of the steel fiber 30 in the illustrated example is linear, but it may also be zigzag, wavy, curved, or other shapes.

[0035] By setting the mixing rate of steel fibers 30 within the range of, for example, 0.3 volume % to 1.0 volume %, it is possible to ensure both the ease of manufacturing segments in a concrete plant and the effect of reinforcing the segments with steel fibers.

[0036] Furthermore, by mixing the steel fibers 30 into the base material, the effect of preventing the machinable segment 10 from becoming a segment in which brittle bending compression fracture or shear fracture occurs first is achieved.

[0037] In addition, reinforcement rods 20 made of glass fiber reinforced plastic or the like are embedded in the base concrete, and a predetermined amount of steel fibers 30 are dispersed therein, resulting in the formation of an easily cuttable segment with high load-bearing capacity and M-φ characteristics superior to those of ordinary RC segments.

[0038] Furthermore, in the easy-to-cut segment 10, a large number of steel fibers 30 are dispersed within the base material, which improves crack dispersion due to the bridging effect of the steel fibers 30, thereby effectively suppressing the crack width of any cracks that do occur.

[0039] Returning to Fig. 1, the easy-to-cut segment 10 has a tenon groove 13 on one ring joint surface 11, and a tenon 14 on the other ring joint surface 11. In the illustrated example, three tenon grooves 13 are provided on one ring joint surface 11, and three tenons 14 are provided on the other ring joint surface 11 at positions corresponding to the three tenon grooves 13. Therefore, the three tenons 14 of one easy-to-cut segment 10 to be joined together engage with the three tenons 13 of the other easy-to-cut segment 10, respectively. Note that the number of tenons 13 and tenons 14 provided on the ring joint surfaces 11 is not limited to the illustrated example.

[0040] At the segment joint surface 12, for example, a butt joint is applied. As shown in FIG. 1, a butt joint is formed by inserting and screwing a resin assembly diagonal bolt 25, also made of resin, into a resin assembly insert 26 embedded in one of the machinable segments 10 from the side of the other machinable segment 10. At the ring joint surface 11, multiple (three in the illustrated example) partial tenon joints can be applied, and the bending moment at the segment joint surface 12 can be effectively transmitted to the adjacent machinable segment 10 via the engagement structure of the tenon 14 and tenon groove 13 of the ring joint surface 11. Note that various types of joints other than butt joints can be applied to the segment joint.

[0041] In addition to the tenon-type joint shown in the drawings, various types of joints may be used as the ring joint, including one-touch joints. For example, in a one-touch joint, the ring joint is formed by, for example, pushing a male joint provided on the ring joint surface of one segment into a female joint provided on the ring joint surface of the other segment. When this type of ring joint is applied to an easily machinable segment, it is preferable that both the female joint and the male joint be made of an easily machinable resin.

[0042] Next, an example of a method for calculating the shear strength of the machinable segment 10 shown in FIG. 1 will be described.

[0043] The shear strength calculation method according to the embodiment calculates the shear strength of concrete in which steel fibers 30 are dispersed: V c is calculated by the following formula (A), and the shear strength shared by the shear reinforcement 22: V s is calculated by the following formula (B), and by adding up both shear strengths, the shear strength of the easy-to-cut segment 10: V u Calculate the following.

[0044]

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[0045]

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[0046] Here, formula (A) is a modified version of the existing formula described in Design Guidelines 1 and 2, while formula (B) is a modified version of the existing formula described here, while referring to Design Guidelines 1. Formula (A) evaluates the reinforcing effect of steel fibers 30 dispersed in concrete by κ (1.0 or more). In addition, β, which evaluates the dowel effect of main reinforcement 21, is also used. p This reflects the elastic modulus of reinforcing bars made of fiber-reinforced plastic (e.g., GFRP), which has a smaller elastic modulus than steel fibers.

[0047] On the other hand, in formula (B), the minimum shear reinforcement mass of the shear reinforcement 22 is determined by applying the minimum shear reinforcement mass specified in Design Guidelines 1 and 3 without increasing the minimum shear reinforcement mass by multiplying it by the inverse of the ratio of the stiffness of the shear reinforcement 22 to the stiffness of the steel bar.

[0048] Specifically, if the stiffness of GFRP reinforcement is 1 / 3 of that of steel bars, as specified in Design Guideline 1, the minimum shear reinforcement amount of 0.15% specified in Design Guideline 3 must be increased according to the stiffness ratio with the steel bars. The elastic modulus of the steel bars is 200N / mm 2 and the elastic modulus of the GFRP rod is 60N / mm 2Since the stiffness ratio of GFRP to steel bars is 0.3, the minimum amount of shear reinforcement should be 0.5%, which is 1 / 0.3 of the 0.15% specified in Design Guideline 3.

[0049] However, if the amount of shear reinforcement is 0.5% or more, the shear reinforcement will be arranged too densely, which will not only increase the production cost of the easy-to-cut segments but will also cause problems such as reduced flowability of concrete during production, which is directly related to the quality of the easy-to-cut segments.

[0050] Therefore, the inventors conducted verification tests, which will be described in detail below, and confirmed that even when rods such as GFRP, which have about one-third the rigidity of ordinary steel bars, are used as shear reinforcement, sufficient shear strength can be obtained with an appropriate amount of shear reinforcement without increasing the amount of shear reinforcement according to its rigidity (elastic modulus). Therefore, in the shear strength calculation method according to the embodiment, even when reinforcing bars made of fiber-reinforced plastic, which have lower rigidity than steel bars (steel), are used as shear reinforcement, the minimum shear reinforcement amount is set to 0.15%, as specified in Design Guidelines 3.

[0051] According to this method for calculating the shear strength of an easily cuttable segment, by properly evaluating the reinforcing effect of the steel fibers 30 dispersed in the concrete and properly evaluating the dowel effect of the main reinforcement 21, it is possible to achieve a rational calculation of the shear strength of an easily cuttable segment in which steel fibers are dispersed in the concrete and shear reinforcement bars with a smaller elastic modulus than steel bars (steel materials) are used.

[0052] [Shear test and results] Next, we will explain the shear tests and their results conducted by the present inventors with reference to Figures 4 to 6. The purpose of this shear test is to verify the validity of calculating the shear strength of easily cuttable segments, in which reinforcing bars made of fiber-reinforced plastic (GFRP) are embedded in concrete, a matrix material in which steel fibers are dispersed, by modifying and combining the shear strength calculation formulas described in the previous Design Guidelines 1, 2, and 3. Furthermore, the purpose of this shear test is to verify the validity of not requiring an increase in the minimum shear reinforcement amount even when the shear reinforcement amount is below the minimum shear reinforcement amount of 0.15% specified in the Design Guidelines 1 and 3.

[0053] <Test Overview> Figure 4 is a schematic diagram of the specimen used in the shear test. As shown in Figure 4, the specimen was a beam member with a square cross section of 250 mm on each side and a length of 1600 mm, and a vertical line load was applied to one point in the center until failure occurred. The shear span ratio was set to 2.8, and five GFRP reinforcement bars (φ25 x 5) were placed as main reinforcement to ensure that shear failure occurred first.

[0054] This shear test is conducted to measure the shear strength of concrete: V c In order to confirm this, CASE1 where no shear reinforcement is placed and CASE2 where the shear reinforcement is placed are compared. s To confirm this, a shear reinforcement ratio of 0.2% (GFRP reinforcement φ8 @ 95 mm) was placed. The test cases are shown in Table 1 below, and the materials used are shown in Table 2 below.

[0055] [Table 1]

[0056] [Table 2]

[0057] <Test Results> The load-displacement relationship obtained from the test is shown in Figure 5, and a comparison of the test results and design values ​​is shown in Table 3 below. Furthermore, the fracture state of the test specimen is shown in Figure 6.

[0058] [Table 3]

[0059] The failure mode in both Case 1 and Case 2 was shear failure due to the opening of diagonal cracks. Furthermore, the maximum load in the test exceeded both the design value and the value calculated based on the actual strength (safety factor was 1.0). The reason that the value calculated based on the actual strength was exceeded is thought to be because the reinforcing effect κ of the mixed steel fibers was 1.0 or more.

[0060] Here, the difference in maximum load between Case 1 and Case 2 was 39 kN. This is equivalent to the calculated shear reinforcement load of 44 kN (312 - 268 = 44 in Table 3), and it has been confirmed that the reinforcing effect of the GFRP shear reinforcement can be appropriately evaluated. Furthermore, due to the inclusion of steel fibers, no brittle fracture was observed even after the maximum load was reached.

[0061] Through this shear test, it was confirmed that the shear strength calculation formula, which adds together formula (A) and formula (B), which is a modified formula obtained by appropriately modifying the shear strength calculation formula described in Design Guidelines 1 and 2, can be applied to easily cuttable segments in which GFRP reinforcement is used as the main reinforcement and shear reinforcement and steel fibers are dispersed within the concrete, both in the case where no shear reinforcement is placed and in the case where 0.2% shear reinforcement is placed.

[0062] Furthermore, it was confirmed that the minimum shear reinforcement content of 0.15% based on Design Guidelines 1 and 3 can be applied without increasing it depending on the stiffness ratio between GFRP and steel bars, and the 0.15% specified in Design Guidelines 3 can be applied.

[0063] It should be noted that the present invention is not limited to the configurations shown here, and other embodiments may be possible in which other components are combined with the configurations described in the above embodiments. In this regard, the present invention can be modified within the scope of the present invention, and can be appropriately determined depending on the application form. [Explanation of symbols]

[0064] 10: Easy-to-cut segment 11: Ring joint surface 12: Segment joint surface 13: Mortise groove 14: Mortice 20: Reinforcement 21: Reinforcement material (main reinforcement) 22: Reinforcement (shear reinforcement) 25: Angled bolt for assembly 26: Assembly insert 30: Steel fiber 31: Central bar 32: Stepped hook material

Claims

1. A method for calculating the shear strength of an easily cuttable segment in which reinforcing bars made of fiber-reinforced plastic are embedded inside concrete, which is a base material, and steel fibers are dispersed inside the base material, and the reinforcing bars include main bars and shear reinforcement bars, The shear strength of the concrete in which the steel fibers are dispersed and the shear strength of the shear reinforcement, which has a smaller elastic modulus than the steel fibers, are calculated separately, and the shear strengths of both are added together to determine the shear strength of the easily cuttable segment; The reinforcing bar is formed of any one of a glass fiber reinforced plastic rod, an aramid fiber reinforced plastic rod, and a medium elasticity carbon fiber reinforced plastic rod; Japan Society of Civil Engineers 2017 Standard Specifications for Concrete A method for calculating the shear strength of easily cuttable segments, characterized by applying the specified minimum amount of shear reinforcement without increasing the minimum amount of shear reinforcement by multiplying the minimum amount of shear reinforcement specified in the [Design Section] by the inverse of the ratio of the stiffness of the reinforcement to the stiffness of the steel bar.

2. the shear strength shared by the concrete in which the steel fibers are dispersed is represented by V ｃ is calculated by the following formula (A), and the shear strength shared by the shear reinforcement: V ｓ is calculated by the following formula (B), and the shear strengths of both are added together to obtain the shear strength of the easy-to-cut segment: V ｕ 2. The method for calculating the shear strength of an easily machinable segment according to claim 1, further comprising the steps of: [Equation 1] [Equation 2]

3. A method for calculating the shear strength of an easily cuttable segment as described in claim 1 or 2, characterized in that the minimum amount of shear reinforcement is a reinforcement ratio of 0.15%, which is the ratio of the cross-section of the shear reinforcement to the cross-section of the concrete.

4. When the reinforcing bar is a glass fiber reinforced plastic rod, the elastic modulus of the reinforcing bar is 200 N / mm ２ Elastic modulus of the glass fiber reinforced plastic rod: 60 N / mm ２ 4. The method for calculating the shear strength of a machinable segment according to claim 3, wherein the ratio is 0.3.

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